Question 1

Given the following molecular formulas, determine the empirical formula of each compound: Cl₂O₅, PbCl₄, N₂O₄, C₃H₆Cl₂.

Accepted Answer

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Question 2

The following minerals contain lead. Rank the minerals in order of percent lead from least to greatest: cottunite, PbCl₂; anglesite, PbSO₄; andorite, PbAgSb₃S₆; and galena, PbS.

Accepted Answer

Galena (PbS) has the highest percentage of lead because it is a simple lead sulfide mineral. Cottunite (PbCl2) has the next highest percentage of lead, followed by anglesite (PbSO4), which has lead combined with sulfur and oxygen, reducing the lead percentage. Andorite (PbAgSb3S6) has the least percentage of lead due to the presence of additional elements like silver (Ag) and antimony (Sb) along with sulfur.

Question 3

How much water had to be added to 50.0 mL of the first solution to obtain the second solution?

Accepted Answer

Since the second solution has half the concentration of the first solution, it means that half of the 50.0 mL must be the solute (assuming that the volume of the solution didn't change when water was added). Therefore, the solute is present in 25.0 mL of the first solution. To make the second solution, we need to dilute the solute with an equal amount of solvent (water). So, we need to add 25.0 mL of water to the 50.0 mL of the first solution, which gives a total volume of 75.0 mL for the second solution. To check that the concentration has halved, we can see that the same amount of solute (represented by 25.0 mL) is now dissolved in 75.0 mL of solution rather than 50.0 mL. 25/75 = 1/3 = 0.333, which is half of the initial concentration of 0.666 M. Therefore, we need to add 25.0 mL of water to the 50.0 mL of the first solution, giving a total volume of 75.0 mL for the second solution. This means that 33.3 mL of water was added to the first solution.

Question 4

Which of the molecules in the figure have an empirical formula that is different from their molecular formula?

Accepted Answer

Only the compounds HSBO, NSBO, and HCOSBO have empirical formulas different from their molecular formulas. The rest of the compounds have the same empirical and molecular formulas. Therefore, choice C is the best answer as it only includes the compounds with different empirical and molecular formulas.

Question 5

Butyric acid has a very unpleasant odor. It is present in some rotting foods, body odor and vomit. Butyric acid has a molar mass of 88.10 g/mol and consists of 54.53% C, 9.153% H, and 36.32% O. What is the molecular formula of butyric acid?

Accepted Answer

The empirical formula is determined by dividing the percentage composition by the atomic masses, resulting in C: 54.53/12.01, H: 9.153/1.008, O: 36.32/16.00. This simplifies to a ratio close to C:4, H:8, O:2, which matches the molecular formula C₄H₈O₂ given the molar mass of 88.10 g/mol.

Question 6

Which of the substances in the figure have the same empirical and molecular formulas?

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Question 7

Given the following molecular formulas, determine the empirical formula of each compound: N₂O₅, PCl₃, H₂O₂, C₆H₄Cl₂.

Accepted Answer

The empirical formula is the simplest whole number ratio of atoms in a compound. For N₂O₅, the ratio cannot be simplified further, so it remains as is. PCl₃ is already in its simplest form. For H₂O₂, the simplest ratio is HO. For C₆H₄Cl₂, the ratio simplifies to C₃H₂Cl, indicating a reduction to the simplest whole number ratio of atoms.

Question 8

Which of the following statements regarding empirical and molecular formulas is correct?

Accepted Answer

To find the molecular formula, divide the molar mass by the empirical formula mass (CH2O = 30 g/mol), which gives 90/30 = 3. Multiply the subscripts in CH2O by 3 to get C3H6O3.

Question 9

Acetaminophen is the active ingredient in Tylenol. It consists of 63.56% C, 6.00% H, 9.27% N, and 21.17% O. What is the empirical formula of acetaminophen?

Accepted Answer

To find the empirical formula, we divide the percentages by the atomic masses of each element (C=12, H=1, N=14, O=16) to get the mole ratio. For C: 63.56/12 ≈ 5.3, H: 6.00/1 = 6, N: 9.27/14 ≈ 0.66, O: 21.17/16 ≈ 1.32. The smallest ratio is approximately 0.66 (for N), so we divide all mole ratios by 0.66 to approximate to the nearest whole number: C ≈ 8, H ≈ 9, N ≈ 1, O ≈ 2. Thus, the empirical formula is C8H9NO2.

Question 10

Calculate the molarity of a solution consisting of 75.0 g of KOH in 2.00 L of solution.

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Question 11

Acetic acid has a molar mass of 60.05 g/mol and consists of 40.00% C, 6.714% H, and 53.29% O. What is the molecular formula of acetic acid?

Accepted Answer

1. Calculate the number of moles for each element: - Carbon (C) : 40.00 g/mol / 12.01 g/mol = 3.332 moles - Hydrogen (H) : 6.714 g/mol / 1.01 g/mol = 6.65 moles - Oxygen (O) : 53.29 g/mol / 16.00 g/mol = 3.33 moles 2. Divide each number of moles by the smallest number of moles to get the mole ratio: - C : 3.332 / 3.33 = 1 - H : 6.65 / 3.33 ≈ 2 - O : 3.33 / 3.33 = 1 3. The empirical formula is thus CH2O. 4. Calculate the empirical formula mass: - ( 1 x 12.01 g/mol ) + ( 2 x 1.01 g/mol ) + ( 1 x 16.00 g/mol ) = 30.03 g/mol 5. Divide the molar mass by the empirical formula mass to get the integer factor: - 60.05 g/mol / 30.03 g/mol = 2 6. Multiply each subscript in the empirical formula by the integer factor to get the molecular formula: - C2H4O2 Therefore, the molecular formula of acetic acid is C₂H₄O₂.

Question 12

Acetic acid is the active ingredient in vinegar. It consists of 40.00% C, 6.714% H, and 53.29% O. What is the empirical formula of acetic acid?

Accepted Answer

To determine the empirical formula, we need to convert the percentage of each element to moles by assuming a 100 g sample.

- 40.00 g C / 12.01 g/mol = 3.33 mol C
- 6.714 g H / 1.01 g/mol = 6.64 mol H
- 53.29 g O / 16.00 g/mol = 3.33 mol O

Next, we divide each mole value by the smallest mole value to get the ratio of atoms. In this case, the smallest mole value is 3.33, so:

- C: 3.33 / 3.33 = 1
- H: 6.64 / 3.33 = 1.99 ≈ 2
- O: 3.33 / 3.33 = 1

Therefore, the empirical formula is CH2O, which corresponds to choice C.

Question 13

How much water had to be added to 10.0 mL of the first solution to obtain the second solution?

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Question 14

The following minerals contain silver. Rank the minerals in order of percent silver from least to greatest: miersite, AgI; hessite, Ag₂Te; empressite, AgTe; and cerargyrite, AgCl.

Accepted Answer

- Miersite (AgI) - only contains one silver atom per molecule, so it has the least amount of silver. - Cerargyrite (AgCl) - contains about 75.3% silver, making it the second least silver-rich mineral. - Hessite (Ag₂Te) - contains around 87.1% silver, so it is the second most silver-rich mineral. - Empressite (AgTe) - has the highest percentage of silver at about 89.2%. Therefore, the correct order from least to most silver would be AgI < AgCl < Ag₂Te < AgTe, which is represented by choice letter E.

Question 15

Methyl butyrate is a compound that is partially responsible for the flavor of apples. It consists of 58.80% C, 9.87% H, and 31.33% O. What is the empirical formula of methyl butyrate?

Accepted Answer

The empirical formula is determined by converting the percentage composition to moles and finding the simplest whole number ratio. For methyl butyrate, the mole ratio of C:H:O is approximately 5:10:2, leading to the empirical formula C₅H₁₀O₂.

Question 16

Calculate the molarity of a solution consisting of 60.0 g of NaOH in 1.50 L of solution.

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Question 17

The molecular formula of the molecules in the figure is:

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Question 18

The following minerals contain zinc. Rank the minerals in order of percent zinc from least to greatest: sphalerite, ZnS; smithsonite, ZnCO₃; zincite, ZnO; gahnite, ZnAl₂O₄.

Accepted Answer

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Question 19

Putrescine is a compound that is partially responsible for the rotten smell of decaying flesh. It consists of 54.50% C, 13.73% H, and 31.77% N. What is the empirical formula of putrescine?

Accepted Answer

To find the empirical formula, we convert the percentages to moles by dividing them by the atomic mass of each element: C (12.01 g/mol), H (1.008 g/mol), N (14.01 g/mol). For C: 54.50/12.01 ≈ 4.54, for H: 13.73/1.008 ≈ 13.62, for N: 31.77/14.01 ≈ 2.27. The ratio of C:H:N is approximately 2:6:1 when divided by the smallest number of moles (2.27). Therefore, the empirical formula is C2H6N.

Question 20

Given the following molecular formulas, determine the empirical formula of each compound: P₄O₁₀, SnCl₂, N₂O₃, CH₃CO₂H.

Accepted Answer

The empirical formula represents the simplest whole-number ratio of atoms in a compound. To determine the empirical formula, we need to divide each subscript by their greatest common factor (GCF). For compound P₄O₁₀: - GCF = 2 - Empirical formula = P₂O5 For compound SnCl₂: - GCF = 1 - Empirical formula = SnCl₂ For compound N₂O₃: - GCF = 1 - Empirical formula = N₂O₃ For compound CH₃CO₂H: - GCF = 1 - Empirical formula = CH₃CO₂H Therefore, the best choice is C as it has the correct empirical formulas for all compounds.

Quiz 4: Chemical Composition

Given the following molecular formulas, determine the empirical formula of each compound: Cl2O5, PbCl4, N2O4, C3H6Cl2.

The following minerals contain lead. Rank the minerals in order of percent lead from least to greatest: cottunite, PbCl2; anglesite, PbSO4; andorite, PbAgSb3S6; and galena, PbS.